I realize that doesn't directly relate to comments, but I think some of the declining quality of conversation owes to the fact that it's getting a bit stale. How many blog articles about productivity can we discuss without some decline?
I don't think we should ban political articles at all. In fact, I think less blog posts about "are we in a bubble?" and more articles on economics, science, philosophy, etc would make HN much more interesting. The median comment here is still of much higher quality than at sites like reddit. And although certain subjects can be sensitive, I doubt that banning these topics will actually reduce meanness, it will just make the change in decorum harder to notice.
Finally, a more extreme idea: why not add a second kind of vote? Perhaps we could vote comments agree/disagree in addition to up or down. These could be right and left arrows, to drive home the point that disagreeing with something ought to be orthogonal to whether it adds to the conversation. We could weigh these votes less, so that rankings more reflect how insightful we think something is, instead of how popular.
- Give more karma to votes on new stories to compensate the extra effort to leave the front page.
- Display one or two random new items on the front page to increase exposure.
- UI change on front page. When mouse moves over the random new item box, display a popup overlaying page containing the new items to allow for upvotes. When mouse moves away, hide the new item page. It's more complicate to implement and might not work too well on phones but should remove the mental barrier to go to the new page.